It is common in the art to wind long pieces of tubular or other extended, linear material onto a spool for storage, transportation and ultimate use.
However, any material that has post-winding shrinkage is subject to profile distortion, if wound directly on a rigid surface, such as a standard spool which has a rigid core.
Thus, for example, in the case of hollow core, polyvinylchloride (PVC) tubular material used, for example, for car seat welting, the material has an inherent tendency to shrink after it has been manufactured. When the material has been wound onto a spool, the shrinkage of the material working against the unyielding, rigid core of the spool, causes the material to become distorted in its profile or cross-sectional shape.
This causes the material to be less desirable or even unusable for its intended use, namely, for example, as car seat welting.